less than/more than +adj 用法

On the other hand, if your language learning has been less than successful, you might do well to try

some of the techniques outlines above.

1）less than +adj 是一种什么结构和用法呢？意思是什么？如何分析less than successful语法成分？

more than 有与此类似的结构用法吗？

2）后面的不定式to try some of...起什么语法作用呢？是条件状语吗？

less than: not completely or not at all

She was less than happy with the results. [=she was not entirely happy or she was unhappy]
He was less than honest in his replies. [=he was not completely honest or he was very dishonest]

◊ A clause that includes more than is often followed by another clause that gives more information or limits the first clause in some way.

I am more than happy to help you, but I'd appreciate being asked politely.
You are more than [=entirely] welcome to stay for dinner, but we aren't having anything special.